( •■^4 ) 



sand vcars ago, is still llicro at llio |>rosoiil day and that llie nu\\ 

 source from Avliicli frcsh-walcr lias hocii sii|>|»li<Ml to llic diliixiiini 

 (the subsoil) has been the duues. 



About tlic Aelocitv Avitli a\ Iiidi ^^ate^ can uiove tlii()u<ili our always 

 very impure clay, wliich i\Ir. dk Hriyn i-iuhtly considers to be a 

 cause of our differeiu'e of opinion, 1 will now slate a few facts and 

 at the same time point out the ai',uiimenls wliich led me to my 

 conception of a diirercnl oriuin of iIk^ deep «ironndwatei- mentioned. 

 First ho\\('\er 1 w isli to point out another |)ossil)le (wiiiin w Inch has 

 not yet been snuueslrMJ and \n hicli cannot be at once I'ejected, and 

 especially a difticulty of a more sei-ious natui-e even than the one 

 objected to my representation ity Mr. dk liRrvx. 



If we assume the exti'emely slow motion ascribed to the uroujid- 

 water by Mr. dk niuvN, it miuht namely l)e that the deep fresh-water 

 under consideration has to be considei'ed as a i-emainder of wlu\t 

 sank a\\ay thci'c centuries a.U'o. I^'oi" not always these jiolders ha\e 

 been siirroinidcd by l)ra('ki>li water oidy. 



Accordinu' to descriptions from the Roman |t(M-iod, Lake Flevo 

 undoubtedly contained walci' IVom the Rhine ajid no salt water as 

 the Zuider/ee does no\\adays. Also the IJ was a freshwater lake 

 commiinicatinii' with the freshwater lakes I'urmer, Woriuer ami 

 Schermer. Moreo\'ei' it is well known that the Haarlem Lake 

 (Haarlemmei-meer) arose by the nnion of at least four lakes: the 

 Old llaailem Lake, the Old Leyden Lake, the Old Lake and the 

 Spiering- Lake which were \'v(\ at least |»artially by one or more 

 branches of the KatANijk Rhine. 'J'he map by Bolstra, the able 

 land-surveyor of IJijnland. pid)lislied in J 745 and incor])0)'ated in 

 ''Present state of the Luitcd Netherlands"'), gives us an idea of the 

 situation of these lakes in J 531 aiid of their gradual union and the 

 enlargement of the Haarlem Lake, originated in this way, down till 

 1740. The waves of this lai-ge lake could easily erode the steep banks, 

 consisting of fen, as Ioav as the same layer of clay which already 

 formed its bottom, the circumstances for this process becoming more 

 and more favourable, chielly on account of the "sinking of the lands" 

 in these parts with res|>ect to the sea, described already a century 

 before the drainiug. This erosion of land occurred at a tremendous 

 rate at the iiorth-east side, where the |K)lders are situated Avhich now 

 have fresh-water in their undergrcumd. Lk Francq van Bkrkhky -') 



ij Tegenwoordige slaat der Vercenigde NederlaiMten. Vol. G p. 163. Amsterdam, 

 I. Tirion. 174G. 



~) J. Lf. Fhancq van Hfukiiky. Nalnniliil\(> Historie van Holland. Vol. [. p. 227. 

 Amsleidam 17G0. 



